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To explore the modification of rheological behavior of fresh cement paste by in situ polymerization, the rheological properties of fresh in situ polymerization modified cement (IPMC) pastes with various acrylamide (AM) monomer dosages and resting time were investigated by rheology test in this paper. The interaction mechanism between inorganic-organic components of IPMC paste and its influence on rheology are also discussed. The results revealed that the yield stress and plastic viscosity of fresh IPMC paste decreased as the AM dosage increased, and rose rapidly with the resting time when the AM dosage was more than 5%. The time-dependent rheological properties of IPMC paste were associated with various periods of AM polymerization reaction. This paper also found that the dispersing effect produced by the AM adsorption and the flocculating effect generated from the polyacrylamide (PAM) microgels bridging would jointly impact the structural buildup of IPMC paste; the former improved the rheological properties and fluidity, while the latter acted contrary. Our results provide the underlying insights needed to guide the dynamic regulation of rheological properties of cement-based materials by in situ polymerization modification. [ABSTRACT FROM AUTHOR]

Structural build-up is of great importance in many concrete applications, such as formwork pressure, multi-layers casting, slip form paving, stability, and 3D printing. In this paper, the growth of static yield stress (τ s ) and thixotropic area were used to characterize the structural build-up of cement paste. The effects of different mineral admixtures, i.e. silica fume (SF), ground slag (GS), fly ash (FA), attapulgite (AG), nano calcium carbonate (NC), and nano silica (NS) on the structural build-up of cement pastes were studied. Calorimetric curves, zeta potential and conductivity of the pastes were also measured. Results showed that thixotropic behavior characterized by the growth of τ s and thixotropic area gave different ranking on cement pastes with various mineral admixtures. NS, AG, NC and SF increased the growth of τ s over 120 min, and NS was the most effective one. FA and GS decreased the growth of τ s over 120 min. Hydration of cement played a dominant role in the structural build-up of cement paste. However, high hydration rate didn’t always lead to high structural build-up rate. [ABSTRACT FROM AUTHOR]

The structural build-up of cement-based materials is often characterized by the determination of the evolution of static yield stress with time. This property is crucial to many applications of concrete. However, the measurement of static yield stress may disturb the structure of cement-based material. As a consequence, the true structural build-up of the materials may not be detected. In this paper, the evolution of static yield stress and storage modulus (G′) determined by small amplitude oscillatory test was determined to characterize the evolution of the structural build-up of cement pastes. Results showed that G′ and static yield stress developed similarly with time. When the tests were carried out on the same sample, the measurement of static yield stress disturbed the structure of cement paste and had a significant effect on the following measurement of G′, but a slight effect on the following measurement of static yield stress. [ABSTRACT FROM AUTHOR]

Air entrainment in cement-based materials is believed to be affected by low air pressure (AP) which is the atmospheric characteristic in high plateaus, and thus the rheology may be affected. This paper attempts to study rheology and air entrainment of fresh Portland cement mortar in simulated low APs. The results indicate that the rheological responses with the varying AP gradients are relevant to the air entrainments in fresh mortar mixtures. The volume changes of air voids in fresh mortars are linearly related to the varying APs, which is owing to not only the AP difference between the inside and outside air voids but also the additional pressure on the liquid films of air voids stemming from the surface tension changes. Moreover, the Bingham capillary number is calculated to account for the air void deformability. Then rheological parameters are correlated to the content and deformability of air voids in fresh mortars. [ABSTRACT FROM AUTHOR]

• The early properties of cement pastes modified by anionic, cationic and nonionic PAM were contrastively studied. • The absorption and hydration of cement pastes with different ionic PAMs were investigated. Polyacrylamide (PAM) has been widely applied as a viscosity modifier to optimize the workability of cement-based materials, but PAMs with different ionic types may show various effects, which is often ignored in practical engineering. In this paper, the early properties including the rheology, flowability, and setting of cement pastes modified by three ionic PAMs (anionic APAM, cationic CPAM, and nonionic NPAM) were contrastively studied. The absorption and hydration of cement pastes with different ionic PAMs were further investigated. Moreover, the contributions of physical flocculation and chemical hydration on the structural build-up of cement pastes were quantified by combining the static yield stress and heat release at the same time scale. The results indicated that three ionic PAMs showed different effects on the structural build-up, fluidity and setting of fresh cement pastes, which were dominated by the different physical flocculation and hydration retardation effects of three ionic PAMs on the cement pastes. The order of flocculation and hydration retardation effects of these three ionic PAMs was APAM ≫ NPAM > CPAM, which was concentration-dependence and evolved over times. The reason is mainly due to the distinct molecular structures and physicochemical properties of three ionic PAMs and their different adsorption behaviors with cements particles. [ABSTRACT FROM AUTHOR]

Pumping changes the rheological properties, workability and construction performance of fresh concrete. However, there were limited knowledges on influences of discharge rates and pumping distances on the fresh properties of concrete. In this paper, effects of various discharge rates and pipeline lengths on rheological properties of self-consolidating concrete (SCC) after pumping were studied. A total of 12 SCC mixtures with the slump flow of 650–745 mm were pumped in pipelines with measured lengths of 342 m, 545 m, and 1044 m by constant discharge rates ranging between 5.1 and 11.4 L/s. Rheological properties were measured before and after pumping. Physical conditions of SCC during pumping, including pressure, shear, and temperature were estimated theoretically and experimentally. Moreover, the total organic carbon in the pore solution of SCC mixtures was measured to evaluate the change of superplasticizer adsorptions after pumping. Test results indicated that, due to pumping, the yield stress increased; the initial tangential viscosity decreased and the shear-thickening phenomenon was eliminated. The changes of yield stresses and viscosity were encouraged by discharge rates. Besides, lower initial slump flow of SCC exhibited a larger slump flow loss after pumping due to a higher shear rate experienced during pumping. The yield stress and viscosity after pumping increased with the increase of pipeline length at similar discharge rates, but decreased with the pipeline length under similar pumping pressures. The adsorption of superplasticizer increased after pumped at relative low discharge rates (5.2–5.7 L/s), but decreased at discharge rates of 7.7–10.8 L/s. [ABSTRACT FROM AUTHOR]

• The rheological properties of LHC pastes with MEA and SRA were studied. • The variations of dynamic yield stress and plastic viscosity were estimated by response surface methodology. • The roles of MEA and SRA on the static yield stress development of LHC pastes were investigated. The combined use of low heat Portland cement (LHC), MgO-based expansive agent (MEA) and shrinkage reducing admixture (SRA) is beneficial to reduce the cracking risk of concrete. In this study, the effects of MEA and SRA on the rheological behaviour of LHC paste were investigated using dynamic and static shearing tests. The response surface methodology was used to estimate the effects of MEA, SRA, and superplasticizer on dynamic rheological parameters, while the zeta potential, calorimetric, and solid phases tests were conducted to explore the mechanisms of time-dependent rheological behaviour. Results indicate that MEA contributes to higher dynamic yield stress and plastic viscosity, while the effect of SRA is dependent on its dosage. MEA promotes the static yield stress development for accelerating the hydration of blends and the formation of Mg(OH) 2. SRA retards the hydration of LHC and blended paste and reduces the number of main hydration products. However, the static yield stress is further increased by SRA, showing a consistent changing trend with the surface area of hydrated particles. [ABSTRACT FROM AUTHOR]

• Resistivity evolution of fresh HSC were measured to characterize the early age hydration process in HSC. • Influence of pumping on early age hydration in HSC were evaluated. • Changes in dynamic yield stress of HSC after pumping were related to corresponding changes in hydration process. The pumping process exerts high pressure and strong shearing on fresh concrete, which may affect the hydration process and rheological behavior of concrete. In this paper, full-scale pumping circuits with lengths of 348-, 600-, and 924-m were established to evaluate the effect of pumping on hydration and rheology of concrete. Electrical resistivity measurement was employed to indirectly evaluate the hydration process of concrete. Ten high-strength concrete (HSC) mixtures with slump flow of 680 ± 50 mm and strength grades of C60-C100 were pumped, and HSC mixtures were sampled before and after pumping for rheological properties and electrical resistivity measurements. Findings indicated that the hydration process, determined by the electrical resistivity evolution, was accelerated after pumping. The end of the dormant period of fresh concrete was decreased by 10.3%-27.3%, and the end of the setting period was shortened by 15.6%-28.4% after pumping. The reduction in the dormant period can be well correlated with the drop in slump flow or increase in dynamic yield stress after pumping. [ABSTRACT FROM AUTHOR]

• The hydration, structural build-up and strength development of cement pates with different accelerators were investigated. • Accelerators increase the structural build-up rate by different mechanisms. • Mechanical efficiency of C-S-H may give wrong ranking on the efficiency of C-S-H. Fast structural build-up and strength development of fresh/hardened cement-based materials are always desired in many scenarios, where accelerators are often used. In this paper, the hydration, structural build-up and strength development of cement pates with different accelerators were investigated. The growth of static yield stress was used to characterize the structural build-up of fresh cement paste with 1% nano silica. Calorimetric curves, zeta potential and conductivity of pastes and strength development of mortars were also measured. Results showed that accelerators promote the reaction of C 3 S or C 3 A at different stages and in different mechanisms. Mechanical efficiency of C-S-H determined by growth of elastic modulus or yield stress over cumulated hydration heat may give wrong ranking on the efficiency of C-S-H. Apart from formation of C-S-H gel, structural build-up may originate from other sources. [ABSTRACT FROM AUTHOR]

• Buildability of 3D printing mortar was evaluated by the deformation of stacking layers. • A deformation monitoring device was designed to monitor the deformation of printing layer. • An equation between the optimal interval time and structural build-up rate was proposed. The buildability of fresh concrete is of great importance to 3D printing technology. In this paper, the buildability of 3D printing mortar was evaluated from the perspective of deformation of fresh mortar during the process of printing. A deformation monitoring device was designed to monitor the change of deformation of printing layer with stacking. The physical and chemical effects on the evolution of structural build-up were evaluated by the growth rate of static yield stress and penetration resistance. Results showed that the chemical effect was more effective than the physical effect, and the combination of physical and chemical effects was the most effective one. The growth of penetration resistance had a linear relationship with the growth of static yield stress, and both of them can be used to characterize the structural build-up of fresh mortar. The deformation value and optimal printing interval time could be obtained by simulating the printing process using the deformation monitoring device. An equation between the optimal interval time and the growth rate of static yield stress was established. [ABSTRACT FROM AUTHOR]

• Time-dependent rheological behavior after continuously shearing was investigated. • A parameter describing the disappearance of shear thinning at down curve was proposed. • Physical and chemical properties affect the evolutions of rheological properties with shearing. Shear history exerts a great impact on the rheological properties, and thus the consolidation and construction quality of concrete. This study experimentally investigated the time-dependent rheological behavior of cementitious pastes under continuously shear mixing. A parameter describing the disappearance of shear thinning at the decelerating curve was proposed. Results indicate that continuous shear mixing could not effectively hinder the development and evolution of thixotropy and yield stress of cementitious pastes over time. After continuously shear mixing for a while, the critical shear rate corresponding to the disappearance of shear thinning increased. Cementitious pastes tended to exhibit shear thinning behavior at relatively lower shear rate ranges. At higher shear rates, the rheological behavior of cementitious pastes after continuously shearing was strongly dependent on the composition of cementitious materials. The evolutions of rheological properties after continuously shearing were associated with the physical nature and chemical hydration of cementitious pastes. [ABSTRACT FROM AUTHOR]

• The rheological properties of AAS pastes have been improved by low surface free energy mineral admixtures. • The surface free energy properties of low surface free energy mineral admixtures have been determined by IGC method. • The interparticle forces were calculated to reveal the mechanism for rheological improvement. This study investigates the effect of low surface free energy mineral admixtures (CaF 2 -dominated fluorite (FL) and fluorine-containing lithium slag (LS)) on the rheological behavior of alkali-activated slag (AAS) pastes. The fluidity, rheological behavior, surface charge properties and surface free energy properties were tested. The interparticle forces based on extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory were calculated to understand the mechanism for the rheological behavior improvement. The results revealed that both FL and LS could improve the fluidity and decrease the yield stress and plastic viscosity of AAS pastes. Furthermore, the attraction is manifested by the sum of electrostatic, van der Waals, and Lewis acid-base forces, and this value decreases with increasing LF or LS content, implying that the particle dispersion in AAS pastes is improved. Furthermore, observing flocculent structures captured by the metallographic microscope proves the better dispersion of AAS pastes after adding FL and LS. Moreover, incorporating LS or FL decreases the flexural and compressive strengths of AAS mortars. [ABSTRACT FROM AUTHOR]

For lightweight chemical foaming mixtures, it is a technical challenge to control the stability while reducing its density. In this study, cenospheres (CP, a lightweight component) was used to replace part of fly ash (FA) to prepare ultra-lightweight foamed geopolymer concrete (UFGC), and the relationship between the fresh properties of the paste and the stability of UFGC mixture were discussed. Results show that incorporating CP to the slag-FA system can effectively reduce the reaction rate and heat release of the geopolymer paste, thereby effectively slowing down the decomposition rate of H 2 O 2. Different from prefabricated foams, the initial size of the foams decomposed by H 2 O 2 is also affected by the fresh properties of the paste. Meanwhile, the float of bubble and the drainage of the paste are controlled by the yield stress of the paste in the stable stage. As the CP substitution ratio increases, the initial yield stress of the paste decreases, which is beneficial to generate smaller initial bubbles. However, for bubbles of the same size, the low yield stress of the paste is detrimental to its long-term stability. Finally, the UFGC mixture with 50% CP has better stability and the best hardened pore structure. In addition, the calculated critical yield stress that prevents the foamed mixture from collapsing is compared with the initial yield stress of the geopolymer paste. [ABSTRACT FROM AUTHOR]

The influence of pumping on the rheological properties of self-consolidating concrete (SCC) is widely recognized, but there is still limited understanding of its behavior within the pipeline. In this study, we propose a novel approach using equilibrium distances to investigate the evolution of rheological properties along the pipeline. Full-scale horizontal pumping circuits spanning 328 m were established to assess the axial development of SCC's rheological properties. Thirteen mixtures, with water-to-cement (w/c) ratios ranging from 0.22 to 0.27, were pumped at discharge rates varying from 5.77 to 12.69 L/s. Our findings show that for pumping setups and material studied, both the w/c ratio of SCC and the discharge rate significantly affected the influence of rheological equilibrium distances on pressure loss gradient changes. In all tested samples, viscosity values required the entire length of the pipeline to reach post-pumping levels, while yield stress values rapidly achieved their fully developed state upon entering the pipeline. Importantly, the predicted pressure loss displayed a strong correlation with experimental measurements, with an accuracy of 89.42% across all tested mixtures. Our predictive model showed an average improvement of 4.6% in accuracy compared to the linear approach, with the most significant enhancement observed in samples with higher w/c ratios. This research sheds new light on the behavior of SCC during pumping and provides valuable insights for optimizing the pumping process. • The equilibrium distance of rheology is introduced to describe SCC flow behavior along the pipeline. • Horizontal pumping circuits spanning 328 m is used. • Factors affecting the equilibrium distance of rheology are discussed. • The prediction accuracy of the model is validated. [ABSTRACT FROM AUTHOR]

• Analytical solution to Couette inverse problem of Herschel-Bulkley fluid was derived. • The transformation equation was validated by both computer synthesized and experimental data. • Comparison between the analytical equation and the approximation equation was conducted. The Herschel-Bulkley model is one of the most commonly used rheological models for Non-Newtonian fluids, and it has been applied to describe the non-linear rheological behavior of fresh concrete. However, because it is difficult to transform the measured rotating speed and torque data into fundamental rheological units for coaxial cylinder rheometers, only an approximate approach has been proposed for this model. In order to improve the accuracy of the solution, a new integral equation describing the torque-rotation speed of Herschel-Bulkley model was derived in this paper, and 40 sets of simulated data were used for the comparison between the two methods. The equation introduced in this study was further validated by the experimental data of SCC. The results indicated that the established solution yielded more accurate results than the approximate one. [ABSTRACT FROM AUTHOR]

The rheological properties of fresh concrete can be characterized by the function between shear rate and shear stress. However, neither shear rate nor shear stress can be measured directly, but transformed from the rotation speed and torque logged by the rheometer. Therefore, the relationship between the rheological model and the torque-rotation speed function needs to be established. In order to describe the nonlinear rheological behavior of fresh concrete, the Robertson-Stiff model was proposed in this paper, and the relationship between rotation speed-torque and rheological parameters measured by the coaxial cylindrical rheometer was derived. Eight concrete mixtures were made, and its rheological properties were tested with ConTec 5 viscometer. Then raw data was utilized to validate the model. The results showed that the Robertson-Stiff model could be used to describe the rheological behavior of fresh concrete. [ABSTRACT FROM AUTHOR]

In this paper, the rheological behavior of blended cements consisting of calcium sulphoaluminate clinker (CSA), ordinary Portland clinker (OPC) and anhydrite (C S ¯) were investigated. The shear stress-shear rate curves of OPC-CSA-C S ¯ blends with different OPC/CSA/C S ¯ ratios were analyzed. Several rheological models were used to fit the rheological curves of cement pastes. The evolution of static yield stress was also monitored to evaluate the structural build-up rate of the blends. Besides, zeta potential measurement, calorimetric test, XRD and TGA analysis were carried out to reveal the physico-chemical kinetics of the rheological evolution of fresh blends. It was found that not only CSH gel but crystals of AFt and gypsum formed at the early age make contributions to the rheological parameters, i.e. plastic viscosity, yield stress and structural build-up. [ABSTRACT FROM AUTHOR]

• The interlayer bonding properties of 3D printing concrete are related to its rheological parameters. • A formula was proposed to quantitatively characterize the relationship between the interlayer bonding strength with the rheological parameters of 3DPC. The rheological behavior of fresh 3D printing concrete (3DPC) not only determines the pumpability, extrudability and buildability, but also strongly affects the interlayer properties. Which is one of the most important characteristics of 3D printing construction that shaped layer by layer. This paper systematically studied the relationship between the rheological behavior (tuned by attapulgite) and the interlayer bonding properties of 3DPC. The results showed that the interlayer bonding strength and interlayer durability strongly depend on the rheological parameters (i.e., dynamic yield stress, plastic viscosity, static yield stress and structural build-up rate). With the increase of dynamic yield stress and structural build-up rate, the interlayer bonding strength and interlayer durability both decreased. Moreover, an empirical formula combining interlayer bonding strength with the dynamic yield stress and the structural build-up rate of 3DPC, considering the porosity and hydration degree, was proposed for the first time. [ABSTRACT FROM AUTHOR]

• Changes in rheological properties of high-strength concrete due to pumping were systemically investigated. • Fresh concrete was sampled in dismantled pipes for the rheological test. • Shear-thickening in high-strength concrete was eliminated after pumping. • Shearing energy during agitation and pumping was estimated and correlated to the changes in viscosity. Pumping of high-strength concrete (HSC) in high-rise or long-span structures is of paramount importance in constructions. However, pumping technology in practice is highly dependent on practical field experience, and full-scale testing that is carried out for complex projects involving new materials or long pumping distances. In this paper, a long pumping circuit was built to study changes in fresh properties of HSC due to pumping. In total, 10 HSC mixtures with strength grades of C60 to C100 were pumped at constant flow rates in pipelines measuring 348, 600 and 924 m in length. Rheological properties, workability characteristics, and concrete temperature were measured on concrete specimens sampled before and after pumping. Rheological properties of concrete sampled in dismantled pipes shortly after the end of pumping were also determined. Test results indicated that the yield stress increased, the initial tangential viscosity decreased and the shear-thickening phenomenon was eliminated due to pumping. The increase in yield stress mostly occurred in the first half of the pipeline, and the tangential viscosity decreased nearly linearly along the pipe length. The levels of drop in initial tangential viscosity were found to positively correspond to the calculated shearing energy, which is estimated given the shear rate, apparent viscosity and elapsed time during agitation and pumping. [ABSTRACT FROM AUTHOR]